1. Field of the Invention
This invention is improved apparatus and an improved method of introducing a pigment into molded plastic articles and more particularly into thermomechanically formed plastic articles.
2. Prior Art
U.S. Pat. No. 3,530,754 teaches an apparatus for introducing pigment concentrate into thermomechanically formed plastic articles. The pigment concentrate is in the form of a long ribbon or strand which is formed from pigment and plastic. At least two pigment strands are fed into a rotary cutting device which continuously cuts off the end of each pigment strand to form sized pigment slices. The pigment slices are stated to have a dimension between 0.001 inch and 0.008 inch. The cutting is achieved by means of a rotary cutting blade working in conjunction with at least two anvils. The pigment strands are cut into slices. Also, the feed rate of the pigment is controlled by the speed of rotation of a feed roller which is operated by a variable speed motor. The amount of pigment cannot be measured by means of a time control which can be preset.
U.S. Pat. No. 2,739,647 discloses an apparatus for simultaneously granulating multiple strips of thermoplastic material for use in an injection molding machine. The ends of the multiple strips are granulated by means of rotating blades. The multiple strips are formed from a continuous sheet which is cut into strips which are of a width regulated by the distance between cutting discs. Very fine grains can be formed, see col. 2, lines 26 to 28, only when the cutting discs have a reduced thickness and when a high speed motor is used with the rotary cutter. So it is seen that very fine grains can only be obtained when only very thin feed material is fed into the rotary cutter.
U.S. Pat. No. 3,529,777 discloses a process of granulating plastic sheets into chips about 1/4 inch wide. The sheet is passed through a pair of meshing cutters which cut through the sheet so as to form the chips. The sheet is not comminuted into a fine powder because the chips must always have one dimension which is equal to the thickness of the original sheet. This patent, at col. 7, lines 36 to 38, speaks of obtaining chips which are about 174 inch wide and, at col. 4, lines 63 to 66, speaks of a sheet feed material which has a thickness of about 0.031 inches. So it is seen that a powder material is not contemplated as being obtainable by this patent. A perforated screen is disclosed which causes recirculation of chopped pieces in order to further reduce their size, but the holes in the screen cannot be much smaller than the size of the original chopped pieces or else the build-up of material will back up to a point where the feed sheet cannot be fed into the multiple chopping blades. The chopped up material just compacts into a mass that results in no material passing through the screen holes. The rotating cutters merely spin without any material being recirculated therebetween. Also, the comminuting is not achieved by directing the sheet directly into a rotating cutter.
U.S. Pat. No. 1,764,202 discloses a device for cutting continuous lengths of yarn, thread or filaments into short lengths by means of an apparatus which utilizes a stationary blade and a revolving blade. U.S. Pat. No. 2,143,252 discloses the use of a shearing device having a rotating blade and a stationary blade having a high natural frequency of oscillation. The shearing device is used to cut threads. U.S. Pat. No. 2,850,421 teaches cutting long, synthetic, extruded fibers into short lengths by means of a rotating, single blade disc which achieves the cutting across (perpendicular to) the direction of travel of the long fibers. U.S. Pat. No. 3,350,971 teaches converting a sheet material into chips.
U.S. Pat. No. 3,811,627, the pertinent portions of which are incorporated herein by reference, teaches the use of particular apparatus and method for mixing a pigment into a plastic, whereby the resulting mixture may be molded or thermomechanically formed into a plastic article. Therein a cutter is described as being a spiral cutter having teeth and a rakelike action. Said U.S. Pat. No. 3,811,627 further discloses a basic apparatus and method for mixing a pigment and plastic pieces which mixture is subsequently fed into a plastic article forming machine.